Marc R. and Whedon hit on a great way to encapsulate the Banner\Hulk dynamic: "The other guy". If you want to think of Banner unleashing his anger as being the rational for the transformation, or MPD, or the creation of two discreet entities from one body, the way they describe it is apt. I just wish we could get Hulk's view of "The Other Guy". That's why he SHOULD have a voice.